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I have seen claims (mostly in the press) that a bike that is "too light" handles poorly on descents, but I don't believe that. Modern bikes, even very light ones, are still pretty stiff compared to older frames. Back in the day I raced a Vitus 979, a far flexier frame than anything sold today. It descended fine for me, and for the large part of the pro peloton who used them, often painted to look like sponsor's bikes. To handle poorly on descents it'd have to be considerably flexier than the Vitus. No one's going to make that.

Straight line speed on descents is affected far more by aerodynamics than by weight. I expect that even mildly aero frames like the Rca are faster down non technical descents than their heavier but less aero predecessors like my R3SL.

However, what I would like to see discussed in more detail is the degree to which limitations on traction are now the key issue.

In summary, is mechanical grip from the bike tyre now the biggest limitation in point to point speed over hills?; given that aerodynamics of wheels and frames and (increasingly) braking performance have significantly outpaced tyre development

Not everything that counts can be counted. Not everything that can be counted counts.

So I'm trying to decide between an Aero and Traditional road bike and noticed that Aeros tend to have a much higher "stack" in their geometry. So I'm both wondering what's the point and also if there's any whitepapers comparing them in the wind tunnel with a dummy rider.

If it turns out the drag is nearly identical due to rider position, I'd much rather have the lighter Traditional road bike for obvious reasons.

So this is hardly scientific, but if I had to guess - stack is higher on some aero frames because it actually does confer an aero advantage. Outside of stem-slamming for the sake of stem slamming, most people run spacers. So, by making the stack higher, it's possible to engineer a frame that is as aero as possible, eliminating the spacers in favor of an aerodynamic shape. I vaguely remember hearing something about this when Cervelo released the S5.

Also, don't forget that it's not JUST the head tube that imparts the aero difference...

johnsaysthisnow wrote:So this is hardly scientific, but if I had to guess - stack is higher on some aero frames because it actually does confer an aero advantage. Outside of stem-slamming for the sake of stem slamming, most people run spacers. So, by making the stack higher, it's possible to engineer a frame that is as aero as possible, eliminating the spacers in favor of an aerodynamic shape. I vaguely remember hearing something about this when Cervelo released the S5.

Also, don't forget that it's not JUST the head tube that imparts the aero difference...

The issue I have is most "aero" modeling of wheels and frames is done at speeds of 25-30 mph or more which seems pro-level fast and losses much of its relevance for anyone averaging speeds slower than that, so its great for the top 5 pct and the rest of us when we get to those speeds but if you average 20-25 over distance it seems the aerodynamics are meaningless, so then weight becomes a bigger factor in terms of hauling and power output. That was my biggest issues with a frame like the BMC TMR01 which I really liked but in the end, felt that they skewed towards stiffness and aero over weight in a way that would not be of much use to me and my decidedly less-than-pro abilities.

Aren't the super tall head tubes actually due to 95% of the customers being lard ass dentists/lawyers/etc. Seriously, if we're talking Specialized, Cervélo, and the likes. This is what I see on the roads on grouprides and the people I meet (pass...) on solo rides, in the case of aero frames.

Ofcourse everyone riding big name aero bikes are neither unfit nor dentists, I'm not looking to hurt anyone's feelings, but the average super dedicated cyclists on WW really doesn't represent what the average real world customer looks like. Most aero road bike buyers are middle-aged (and then some...), unfit by serious cyclist terms, holds down a well paying occupation, and are dead slow on a bike...

Cervélo and Specialized can't ofcourse say this in an ad blurb, but reality is likely they are not making bikes for cyclists - they are making bikes for customers. These are the primary customers.

I think doe frames were designed for this types of riders like the cervelo Rs was, but it also makes sense that rider positioning has evolved over time and a more comfortable, slightly more upright position is beneficial for most, it also helps to not be too stretched out as ar as power transfer on a bike, so taller head tubes are stiffer and potentially can be designed more aerodynamically than spacers. Riders who stack lots of spacer on top of taller head tubes are probably riding the wrong type of frame. At least thats my understanding.

gitsome wrote:The issue I have is most "aero" modeling of wheels and frames is done at speeds of 25-30 mph or more which seems pro-level fast and losses much of its relevance for anyone averaging speeds slower than that, so its great for the top 5 pct and the rest of us when we get to those speeds but if you average 20-25 over distance it seems the aerodynamics are meaningless, so then weight becomes a bigger factor in terms of hauling and power output. That was my biggest issues with a frame like the BMC TMR01 which I really liked but in the end, felt that they skewed towards stiffness and aero over weight in a way that would not be of much use to me and my decidedly less-than-pro abilities.

Why does aerodynamics go out the door when you are doing 20-25mph instead of 25-30mph?

As Zipp and some other guys have shown, if you are a slower rider (20-25mph) you are out on the course longer so you actually benefit more in the amount of time saved vs running something not as aero.

"Marginal gains are the only gains when all that's left to gain is in the margins."